In Which I Get To Use My Own Work


We have goldfish, normally kept in an outdoor pond. It’s not a deep enough pond that it would be safe to leave them out for a very harsh winter. So we keep as many as we can catch in a couple 150-gallon tanks in the basement.

Recently, and irritatingly close to when we’d set them outside, the nitrate level in the tanks grew too high. Fish excrete ammonia. Microorganisms then turn the ammonia into nitrates and then nitrates. In the wild, the nitrates then get used by … I dunno, plants? Which don’t thrive enough hin our basement to clean them out. To get the nitrate out of the water all there is to do is replace the water.

We have six buckets, each holding five gallons, of water that we can use for replacement. So there’s up to 30 gallons of water that we could change out in a day. Can’t change more because tap water contains chloramines, which kill bacteria (good news for humans) but hurt fish (bad news for goldfish). We can treat the tap water to neutralize the chloramines, but want to give that time to finish. I have never found a good reference for how long this takes. I’ve adopted “about a day” because we don’t have a water tap in the basement and I don’t want to haul more than 30 gallons of water downstairs any given day.

So I got thinking, what’s the fastest way to get the nitrate level down for both tanks? Change 15 gallons in each of them once a day, or change 30 gallons in one tank one day and the other tank the next?

Several dozen goldfish, most of them babies, within a 150-gallon rubber stock tank, their wintering home.
Not a current picture, but the fish look about like this still.

And, happy to say, I realized this was the tea-making problem I’d done a couple months ago. The tea-making problem had a different goal, that of keeping as much milk in the tea as possible. But the thing being studied was how partial replacements of a solution with one component affects the amount of the other component. The major difference is that the fish produce (ultimately) more nitrates in time. There’s no tea that spontaneously produces milk. But if nitrate-generation is low enough, the same conclusions follow. So, a couple days of 30-gallon changes, in alternating tanks, and we had the nitrates back to a decent level.

We’d have put the fish outside this past week if I hadn’t broken, again, the tool used for cleaning the outside pond.

Author: Joseph Nebus

I was born 198 years to the day after Johnny Appleseed. The differences between us do not end there. He/him.

3 thoughts on “In Which I Get To Use My Own Work”

  1. What do the fish say when you ask them “Do you guys want tea or milk added to your pond?” Do you still have the one that does his Ed McMahon impression “Heeeeeeeeeeeeeeeere’s Johnny!” when he sees you coming down the path?

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    1. I never ask the fish about anything added to the pond, because they get all worked up about the chemistry involved. And I understand their concerns, since they have to equilibrate with the stuff, but when it’s, like, four tablespoons of aquarium salt? What do I say? How do I know what’s in aquarium salt? Who has any idea what that stuff is?

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